Protective layers and methods of formation during plasma etching processes

ABSTRACT

A method of plasma etching includes receiving, by a plasma processing apparatus, a substrate into a processing chamber of the plasma processing apparatus. The substrate includes an etchable layer and a first mask layer overlying the etchable layer. The first mask layer includes a plurality of openings vertically aligned with exposed regions of the etchable layer. The method further includes forming, in the processing chamber, a protective layer over the first mask layer and the exposed regions and etching, in the processing chamber, the protective layer and the exposed regions to remove the protective layer and form recesses in the etchable layer.

TECHNICAL FIELD

The present invention relates generally to methods of plasma etchingincluding formation of protective layers, and, in particularembodiments, to structures of protective layers for use during plasmaetching processes, and methods of formation during plasma etchingprocesses.

BACKGROUND

Device formation within microelectronic workpieces may involve a seriesof manufacturing techniques including formation, patterning, and removalof a number of layers of material on a substrate. Plasma processes suchas plasma etching processes are commonly used to form devices inmicroelectronic workpieces. As structure size decreases and density ofstructures increases, desired pattern fidelity may be become moredifficult to guarantee during plasma etching processes.

Etch selectivity is important during plasma etching to increase patternfidelity for a variety of reasons. For example, higher etch selectivitydecreases optimal mask thickness, increases productivity, maintainspattern integrity during the etching process, improves etch profile, andreduces the likelihood of merged patterns and/or line breaks. Changingthe chemical composition of the mask is one way to increase etchselectivity. However, changing the chemical composition of the mask maynegatively impact other aspects of the fabrication process such asincreasing cost, reducing throughput, or remove process compatibility.

Another possible method of improving etch selectivity is to change ortune the plasma etching process. For example, continuous wave plasmaetching processes may be replaced with atomic layer etching (ALE)processes. Yet, ALE processes require additional processing steps tomodify each atomic layer that is etched resulting in reduced throughput.Tuning plasma etching processes for increased etch selectivity alsotypically results in longer process times because slower processes canbe more selective. For example, lower ion bombardment energy canimproved selectivity, but will decrease throughput. Further, processtuning for selectivity may have tradeoffs (sidewall profile anglemodification, critical dimension, damage, etc.). Therefore, it may bedesirable to improve etch electivity during plasma etching processeswithout changing the mask film type and while maintaining the desiredlevels of throughput and the final feature characteristic (angle,critical dimension, etc.).

SUMMARY

In accordance with an embodiment of the invention, a method of plasmaetching includes receiving, by a plasma processing apparatus, asubstrate into a processing chamber of the plasma processing apparatus.The substrate includes an etchable layer and a first mask layeroverlying the etchable layer. The first mask layer includes a pluralityof openings vertically aligned with exposed regions of the etchablelayer. The method further includes forming, in the processing chamber, aprotective layer over the first mask layer and the exposed regions andetching, in the processing chamber, the protective layer and the exposedregions to remove the protective layer and form recesses in the etchablelayer.

In accordance with another embodiment of the invention, a method ofplasma processing includes forming a protective layer over a patternedmask layer and exposed regions of an etchable layer of a substrate. Theprotective layer includes a first thickness measured from upper surfacesof the patterned mask layer and a second thickness measured from exposedsurfaces of the exposed regions. The first thickness is greater than thesecond thickness. The method further includes concurrently removing theprotective layer and etching the etchable layer of the substrate at theexposed regions. The steps of forming the protective layer, removing theprotective layer, and etching the etchable layer are performed in-situduring a plasma etch.

In accordance with still another embodiment of the invention, a methodof plasma processing includes providing a substrate comprising anetchable layer and a patterned mask layer overlying the etchable layerand forming an in-situ protective layer over the patterned mask layerand exposed regions of the etchable layer. The patterned mask layerincludes a dielectric hard mask, an upper hard mask overlying thedielectric hard mask, and a plurality of openings vertically alignedwith the exposed regions of the etchable layer. The upper hard maskincludes a metal, metal oxide, or a metal nitride. The method furtherincludes performing a plasma etching step including etching the exposedregions of the etchable layer, removing the in-situ protective layer,and retaining the upper hard mask and the dielectric hard mask.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIGS. 1A and 1B illustrate a conventional method of plasma etching,where FIG. 1A illustrates a conventional workpiece prior to etching andFIG. 1B illustrates the conventional workpiece after etching;

FIGS. 2A, 2B, and 2C illustrate an example method of plasma etching inaccordance with an embodiment of the invention, where FIG. 2Aillustrates a patterned mask layer overlying an etchable layer, FIG. 2Billustrates a protective layer formed over the patterned mask layer andthe etchable layer, and FIG. 2C illustrates the patterned mask layer andthe etchable layer after an etching process;

FIGS. 3A, 3B, and 3C illustrate another example method of plasma etchingin accordance with an embodiment of the invention, where FIG. 3Aillustrates a first mask layer and a second mask layer overlying anetchable layer, FIG. 3B illustrates a protective layer formed over thefirst mask layer, the second mask layer, and the etchable layer, andFIG. 3C illustrates the first mask layer, the second mask layer, and theetchable layer after an etching process;

FIGS. 4A, 4B, and 4C illustrate still another example method of plasmaetching in accordance with an embodiment of the invention, where FIG. 4Aillustrates an etchable layer including recesses vertically aligned withopenings in an overlying patterned mask layer, FIG. 4B illustrates aprotective layer formed over the patterned mask layer and the recessesof the etchable layer, and FIG. 4C illustrates the patterned mask layerand the etchable layer after an etching process;

FIG. 5 illustrates a flowchart of an example method of plasma etching inaccordance with an embodiment of the invention; and

FIG. 6 illustrates a flowchart of another example method of plasmaetching in accordance with an embodiment of the invention.

Corresponding numerals and symbols in the different figures generallyrefer to corresponding parts unless otherwise indicated. The figures aredrawn to clearly illustrate the relevant aspects of the embodiments andare not necessarily drawn to scale. The edges of features drawn in thefigures do not necessarily indicate the termination of the extent of thefeature.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of various embodiments are discussed in detailbelow. It should be appreciated, however, that the various embodimentsdescribed herein are applicable in a wide variety of specific contexts.The specific embodiments discussed are merely illustrative of specificways to make and use various embodiments, and should not be construed ina limited scope.

Conventional methods of plasma etching may have a variety ofdisadvantages related to etch selectivity. For example, the edges of agiven mask may be particularly susceptible to negative effects ofreduced etch selectivity due to increased surface area available foretching. The result is a higher etch rate at the mask edges leading toedge rounding and, eventually, to reduction in the dimensionality of themask pattern. Reduced mask dimensionality due to inadequate etchselectivity may resulting in merged patterns and/or line breaks andeventually pattern loss.

However, even if the dimensionality of the mask features remains intact,rounded feature edges may still induce negative effects on the finaletch such as tapered etch profiles and footing. In cases where multiplemask layers are utilized, underlying mask material may also bedisadvantageously removed which may negatively impact current and futureetching processes.

Since corners represent the intersection of feature edges, cornerselectivity may be especially important when attempting to improvepattern fidelity. At smaller feature sizes, corners become a largerpercentage of the total and features may be more easily merged duringthe etching process. For example, small holes and thin lines may beparticularly susceptible to merging or breaking due to low cornerselectivity.

As mentioned above, conventional methods of improving etch selectivitymay disadvantageously affect throughput, process compatibility, cost,and feature integrity. For example, ALE processes and quasi-ALE (QALE)processes may be very slow compared to continuous wave etchingprocesses, but may improve etch selectivity. Yet, even changing ortuning the plasma etching process may still not result in desiredfeature profile, critical dimension (CD), layer damage, and the like.Changing the mask film type may increase cost, decrease throughput, or,in some cases, not be a viable option due to process compatibilityconsiderations.

FIGS. 1A and 1B illustrate a conventional method of plasma etching,where FIG. 1A illustrates a conventional workpiece prior to etching andFIG. 1B illustrates the conventional workpiece after etching. Theconventional method of plasma etching described in the following isincluded to provide context for comparison purposes and represents asingle example of a disadvantageous conventional method of plasmaetching which may be improved upon by the embodiments described herein.

Referring to FIG. 1A, a conventional workpiece 100 includes an ultralow-κ (ULK) dielectric layer 102 formed on a metallization layer 101. Adense dielectric layer 103 and a titanium nitride (TiN) layer 104 arepatterned to include openings 105 and disposed on the ULK dielectriclayer 102.

Referring to FIG. 1B, a plasma etching process is performed on theworkpiece boo resulting in removal of material of the ULK dielectriclayer 102, the dense dielectric layer 103, and the titanium nitridelayer 104. Due to the etch selectivity being disadvantageously low, theplasma etching process alters the shape of the dense dielectric layer103, and the titanium nitride layer 104 to form a rounded TiN layer 107.The rounded TiN layer 107 allows the plasma etching process to alsoremove material from the dense dielectric layer 103 which forms acompromised dense dielectric layer 106.

The resulting profile of the compromised dense dielectric layer 106 andthe rounded TiN layer 107 adversely affects the conventional method ofplasma etching leading to the formation of suboptimal recesses 108 inthe ULK dielectric layer 102. The suboptimal recesses 108 include one ormore of the disadvantages described above due to the excessive removalof material from the dense dielectric layer 103, and the titaniumnitride layer 104.

In various embodiments, a method of plasma etching includes forming aprotective layer over a mask layer and an underlying etchable layer. Theprotective layer is formed in-situ during the plasma etching process ina processing chamber of a plasma processing apparatus. The protectivelayer is subsequently removed during a plasma etch of the etchablelayer.

The embodiments described herein may advantageously increase etchselectivity of mask layer during the etching process. For example, thecorner selectivity during the etching process may be improved. Theformation of the protective layer in-situ may advantageously improvethroughput of the plasma etching process compared to conventional plasmaetching processes. The protective layer may also beneficially affordincreased flexibility in the selection of the film type of the masklayer and the type of etching process (e.g., enable continuous waveprocesses with good selectivity).

Embodiments provided below describe various structures and methods offorming a protective layer, and in particular, a protective layer formedin-situ during a plasma etching process. The following descriptiondescribes the embodiments. An example method of plasma etching includingforming a protective layer is described using FIGS. 2A, 2B, and 2CB. Twoadditional example methods of plasma etching are described using FIGS.3A, 3B, and 3C and FIGS. 4A, 4B, and 4C. Two further example methods ofplasma processing are described using flowcharts in FIGS. 5 and 6.

The following embodiment methods of plasma etching may be advantageouslyapplicable at all stages of semiconductor device fabrication. Forexample, the methods of plasma etching described herein may apply toback-end-of-line (BEOL) processing (e.g. metallization,interconnections, contacts, etc.). Additionally, these embodimentmethods may also apply to front-end-of-line (FEOL) processing (e.g.devices) and/or middle-of-line (MOL) processing (e.g. device contacts).

FIGS. 2A, 2B, and 2C illustrate an example method of plasma etching inaccordance with an embodiment of the invention, where FIG. 2Aillustrates a patterned mask layer overlying an etchable layer, FIG. 2Billustrates a protective layer formed over the patterned mask layer andthe etchable layer, and FIG. 2C illustrates the patterned mask layer andthe etchable layer after an etching process.

Referring to FIG. 2A, a workpiece 200 at an initial stage of a method ofplasma etching includes an etchable layer 20 overlying a substrate 10.The substrate 10 may be any suitable material or combination ofmaterials at any stage of processing. In various embodiments, thesubstrate 10 includes underlying layers. In some embodiments, theunderlying layers include a metallization layer and include a backsidemetallization layer in one embodiment. The underlying layers may includea metal level zero (M0) or a metal level one (M1), for example. Inanother embodiment, the underlying layers include device layers. Invarious embodiments, the substrate 10 includes a semiconductor material.In one embodiment, the substrate 10 is a wafer.

The etchable layer 20 may directly contact the substrate 10 as shown.Alternatively, additional layers may be included between the substrate10 and the etchable layer. The etchable layer 20 is a layer configuredto be etched by the method of plasma etching. In various embodiments,the etchable layer 20 includes a dielectric (e.g., an oxide, a nitride,etc.), and is a low-κ dielectric or ULK dielectric in some embodiments.In some embodiments, the etchable layer 20 is a semiconducting material.For example, the etchable material may be silicon, germanium, a III-Vsemiconductor, a II-VI semiconductor, and the like. In otherembodiments, the etchable layer 20 may include a metal such as aluminum,copper, tungsten, and others.

A patterned mask layer 230 overlies the etchable layer 20. The patternedmask layer 230 may be formed using any suitable combination ofdeposition method, growth technique, lithographic technique, directwrite method, multi-patterning techniques, and others. In oneembodiment, the patterned mask layer 230 is a later of a singlematerial. In other embodiments, the patterned mask layer 230 includesmultiple layers of similar or different materials. For example, thepatterned mask layer 230 may include dielectric materials, metalmaterials, and/or semiconductor materials. In various embodiments, thepatterned mask layer 230 includes a dielectric layer and includes anoxide or a nitride in some embodiments. In one embodiment, the patternedmask layer 230 includes a ceramic material. The patterned mask layer 230includes a first vertical thickness 263 measured vertically from theetchable layer 20 as illustrated.

The patterned mask layer 230 is patterned to include features with uppersurfaces 234 defining openings 32 that are vertically aligned withexposed regions 22 of the etchable layer 20. The exposed regions 22include exposed surfaces 24 of the etchable layer 20. The openings 32may include any suitable shape when viewed from above. In oneembodiment, the openings 32 include lines (e.g. features with a singledimension larger than the minimum feature size). In one embodiment, theopenings 32 include holes (e.g. features of minimum size).

The workpiece 200 may be provided as described at the initial stage of amethod of plasma etching. That is, the workpiece 200 may be receivedinto a processing chamber of a plasma processing apparatus asillustrated in FIG. 2A, with openings 32 that reveal exposed surfaces 24of an etchable layer 20 supported by a substrate 10. A vacuum suitablefor plasma etching processes may then be created in the processingchamber and may be maintained (e.g. not broken) until after theconclusion of the plasma etching process. Specifically, although thepressure inside the processing chamber may fluctuate during the methodof plasma etching, the pressure is always lower than the ambientpressure outside the processing chamber.

Referring to FIG. 2B, the workpiece 200 is shown after the formation ofa protective layer 40. The protective layer 40 overlies both thepatterned mask layer 230 and the etchable layer 20. The protective layer40 is formed in-situ (i.e. in place) during the method of plasmaetching. For example, the workpiece 200 may be a processing chamber asdescribed above prior to the formation of the protective layer 40. Theworkpiece 200 is not removed from the processing chamber in order toform the protective layer 40. Rather, the protective layer 40 is formedin-situ in the processing chamber. Therefore, the protective layer 40 isan in-situ protective layer.

The protective layer 40 may have a higher etch selectivity than theetchable layer 20 to a particular etchant used to etch the etchablelayer 20. For example, the etchant may etch the etchable layer 20 at ahigher rate than the protective layer 40. The protective layer 40 may bea conformal layer in some embodiments. However, the thickness of theprotective layer 40 is different above the upper surfaces 234 than abovethe exposed surfaces 24. For example, the protective layer 40 has afirst thickness 61 above the upper surfaces 234 and a second thickness62 above the exposed surfaces 24. In various embodiments, the firstthickness 61 is greater than the second thickness 62. In someembodiments, the first thickness 61 is between about 1 nm and about 10nm and is about 5 nm in one embodiment. The protective layer 40 isillustrated as forming on sidewalls of the patterned mask layer 230, butthere is no requirement for this to be the case.

The protective layer 40 may be formed using any suitable process in-situin the processing chamber. For example, the protective layer 40 may beformed using methods such as silicon precursor techniques (e.g. usingSiCl₄, SiF₄, etc.), in-situ atomic layer deposition (ALD), sputterdeposition, plasma polymerization (e.g. using precursors such as CH₄,etc.), direct current superposition (DCS) techniques, and the like. Invarious embodiments, the protective layer 40 is formed in less thanabout 60 s. In some embodiments, the protective layer 40 is formed inbetween about 10 s and 60 s. In one embodiment, the protective layer 40is formed in about 20 s. Alternatively, the protective layer 40 may beformed over a time period longer than 60 s.

The protective layer 40 may include any suitable material, the choice ofwhich may depend on the details of a given process such as etch type,composition of the etchable layer 20, composition of the patterned masklayer 230, throughput requirements, cost, complexity, and others. Forexample, the protective layer 40 may include silicon (e.g. may besilicon (Si), silicon oxide (SiO₂), silicon nitride (Si₃N₄), etc.). Invarious embodiments, the protective layer 40 includes an organicmaterial such as an organic polymer. In some embodiments, the protectivelayer 40 is a fluorocarbon polymer.

Referring to FIG. 2C, the workpiece 200 includes recesses 250 in theetchable layer 20 after a plasma etching step is performed. The plasmaetching step may utilize any suitable plasma etching technique. In oneembodiment, the plasma etching step includes a continuous wave plasmaetching technique. A continuous wave plasma etching step in combinationwith the protective layer 40 may advantageously improve etch selectivitywhile increasing throughput over conventional plasma etching methods. Inaddition, ALE or QALE may be used.

The protective layer 40 is fully removed while the patterned mask layer230 and the etchable layer 20 are each partially removed. The partialremoval of the etchable layer 20 results in the recesses 250. Thepartial removal of the patterned mask layer 230 reduces the thickness toa second vertical thickness 264. For reference purposes portions of theetched protective material 41 and the etched mask material 231 are shownusing dotted lines.

The majority of the patterned mask layer 230 remains after the etchingstep. For example, in various embodiments, the second vertical thickness264 is greater than 50% of the first vertical thickness 263.Additionally, the corner selectivity of the patterned mask layer 230 isadvantageously improved using the protective layer 40 compared toconventional processes. For example, the shape of the corners of thepatterned mask layer 230 is less rounded than those of conventionalmethods of plasma etching (as shown in FIG. 1B). The improvedselectivity afforded by the use of the protective layer mayadvantageously improve one or a combination of the pattern integrityduring the etching step, fidelity of the transferred pattern, improved(e.g. straighter) profile of the recesses 250, reduction or eliminationof footing and other undesirable etching artifacts.

The recesses 250 include a vertical depth 65 and a first lateral width66. The dimensions as illustrated are by way of example only. There areno requirements for the dimensions of any one recess to be equal toanother. However, as described previously, corner selectivity may bemore important for small feature sizes and/or dense patterns. Therefore,in specific cases, the patterned mask layer 230 may include regularlyspaced recesses 250 that each include the first lateral width 66 andseparated by a second lateral width 67, for example. Both the firstlateral width 66 and the second lateral width 67 may be small. In someembodiments one or both of the first lateral width 66 and the secondlateral width 67 are less than about 25 nm. In one embodiment, the firstlateral width is about 20 nm. Similarly, in one embodiment, the secondlateral width is about 20 nm.

As noted previously is relation to the shape of the openings 32, therecesses 250 may have any suitable shape such as lines, holes, etc. Theaspect ratio of the recesses 250 may be large. For example, the recesses250 may be deep trenches. In some embodiments, the vertical depth 65 islarger than the first lateral width 66. In one embodiment, the verticaldepth 65 is greater than or equal to about twice the first lateral width66. In various embodiments, the vertical depth 65 is between about 35 nmand about wo nm and is about 40 nm in one embodiment.

FIGS. 3A, 3B, and 3C illustrate another example method of plasma etchingin accordance with an embodiment of the invention, where FIG. 3Aillustrates a first mask layer and a second mask layer overlying anetchable layer, FIG. 3B illustrates a protective layer formed over thefirst mask layer, the second mask layer, and the etchable layer, andFIG. 3C illustrates the first mask layer, the second mask layer, and theetchable layer after an etching process. The example method of plasmaetching as illustrated in FIGS. 3A, 3B, and 3C may be a specificimplementation of other embodiment methods of plasma etching such as themethod of plasma etching described using FIGS. 2A, 2B, and 2C, forexample. Similar labels may be as previously described.

Referring to FIG. 3A, a workpiece 300 at an initial stage of a method ofplasma etching includes an etchable layer 20 overlying a substrate 10. Afirst mask layer 336 is included overlying the etchable layer 20. Thefirst mask layer 336 includes a first vertical thickness 363 asillustrated. The first mask layer 336 may include a metal such as atransition metal (e.g. titanium, ruthenium, hafnium, etc.). In someembodiments the first mask layer 336 is a nitride while in otherembodiments the first mask layer 336 is an oxide. In some cases, thefirst mask layer 336 may be considered an upper hard mask. In oneembodiment, the first mask layer 336 is a titanium nitride (TiN) layer.The first mask layer 336 may also be a titanium oxide layer, rutheniumoxide, hafnium oxide, among others.

A second mask layer 338 may be included between the first mask layer 336and the etchable layer 20. For example, the second mask layer 338 maycomprise a dielectric material. In some such cases, the second masklayer 338 may be considered a dielectric hard mask. In one embodiment,the second mask layer 338 includes an oxide. In another embodiment, thesecond mask layer 338 includes a nitride. In various embodiments, thesecond mask layer 338 includes a low-κ dielectric material and is adense ULK dielectric material in one embodiment. Optionally, the secondmask layer 338 may be omitted and only the first mask layer 336 isincluded. For example, a hard mask including a transition metal may beused as a solo mask layer.

Referring to FIGS. 3B and 3C, a protective layer 40 is formed in-situ aspreviously described. The protective layer 40 is subsequently removed ina plasma etching step. As before, portions of the etchable layer 20 areremoved during the plasma etching step to form recesses 250 in theetchable layer 20. A portion of the first masking layer 336 includingetched mask material 331 is also removed during the plasma etchingprocess resulting in a second vertical thickness 364 of the first masklayer 336. However, the second mask layer 338 is advantageouslysubstantially unaffected by the plasma etching step as shown.

As before, the majority of the first mask layer 336 may remain after theplasma etching step. For example, the second vertical thickness 364 maybe greater than 60% of the first vertical thickness. This is in contrastto conventional methods of plasma etching such as, for example, theconventional method illustrated and described using FIGS. 1A and 1Bwhere the dense dielectric layer 103 underlying the titanium nitridelayer 104 is undesirably eroded by the plasma etching step.

FIGS. 4A, 4B, and 4C illustrate still another example method of plasmaetching in accordance with an embodiment of the invention, where FIG. 4Aillustrates an etchable layer including recesses vertically aligned withopenings in an overlying patterned mask layer, FIG. 4B illustrates aprotective layer formed over the patterned mask layer and the recessesof the etchable layer, and FIG. 4C illustrates the patterned mask layerand the etchable layer after an etching process. The example method ofplasma etching as illustrated in FIGS. 4A, 4B, and 4C may be a specificimplementation of other embodiment methods of plasma etching such as themethod of plasma etching described using FIGS. 2A, 2B, and 2C, forexample. Similar labels may be as previously described.

Referring to FIG. 4A, a workpiece 400 at an initial stage of a method ofplasma etching includes an etchable layer 20 overlying a substrate 10.Additionally, recesses 450 are already formed in the etchable layer 20at this initial stage. The recesses 450 have an initial vertical depth465. A patterned mask layer 230 is includes overlying the etchable layer20 and may be as previously described.

Referring to FIG. 4B, a protective layer 40 is formed in-situ over thepatterned mask layer 230 and the recesses 450. The formation of theprotective layer 40 may be as previously described. In some embodiments,the recesses 450 may be sufficiently narrow and/or deep so that materialof the protective layer 40 does not reach some or all of the exposedsurfaces 24 of the etchable layer 20.

Referring to FIG. 4C, a plasma etching step is performed to remove theprotective layer 40 and deepen the recesses 450 so that the initialvertical depth 465 is increased to an extended vertical depth 468. Invarious embodiments, the step of forming a protective layer prior to theworkpiece 400 as shown in FIG. 4B may be repeated after the plasmaetching step. For example, another protective layer may be formed overthe patterned mask layer 230 and the recesses 450 having the extendedvertical depth 468. An additional plasma etching step may then beperformed to remove additional material (illustrated as dashed linesbelow the recesses 450 in FIG. 4C) from the etchable layer 20 whilestill maintaining integrity of the patterned mask layer 230. Thistwo-step in-situ cycle of protection layer formation followed by aplasma etching step may be repeated as desired to increase the depth ofthe recesses 450.

FIGS. 5 and 6 illustrate flowcharts of example methods of plasma etchingin accordance with embodiments of the invention. Arrows in the flowchartare intended to indicate an order of performing the method steps unlessotherwise indicated. Additional steps may be performed between methodsteps as described and also as will be apparent to one of ordinary skillof the art without departing from the scope of the invention.

Referring to FIG. 5, a method 500 of plasma etching includes a step 501of receiving a substrate into a processing chamber of a plasmaprocessing apparatus. The substrate includes an etchable layer and afirst mask layer overlying the etchable layer. The first mask layerincludes a plurality of openings vertically aligned with exposed regionsof the etchable layer. The processing chamber receives the substrate asan initial step in the method 500 of plasma etching.

The substrate may also include a second mask layer between the firstmask layer and the etchable layer. The openings may then extend throughboth the first mask layer and the second mask layer. In one embodiment,the first mask layer comprises a transition metal. In one embodiment,the second mask layer comprises a dielectric.

The method 500 further includes a step 502 of forming, in the processingchamber, a protective layer over the first mask layer and the exposedregions. Step 502 is performed after step 501 without removing thesubstrate from the processing chamber. Other steps may also be performedbetween step 501 and step 502, but the substrate is not removed from theprocessing chamber between step 501 and step 502. For example, a step ofetching, in the processing chamber, the exposed regions of the etchablelayer after receiving the substrate in step 501 and before forming theprotective layer in step 502 may be performed to form initial recessesin the etchable layer.

After forming the protective layer, the method 500 includes a step 503of etching, in the processing chamber, the protective layer and theexposed regions to remove the protective layer and form recesses in theetchable layer. Before forming the protective layer in step 502, themethod may also include a step of creating a vacuum in the processingchamber. Both forming the protective layer in step 502 and etching theprotective layer and the exposed regions in step 503 may be performedwithout breaking the vacuum.

Step 502 and step 503 may be cyclically performed without removing thesubstrate from the processing chamber. For example, after performingstep 503, a subsequent iteration of step 502 of forming, in theprocessing chamber an additional protective layer over the first masklayer and the recesses in the etchable layer may be performed followedby another iteration of step 503 of etching, in the processing chamber,the additional protective layer and the etchable layer in the recessesto remove the additional protective layer and increase a vertical depthof the recesses. This cycle may be repeated to increase the verticaldepth of the recesses while advantageously reducing damage to the masklayer.

Referring now to FIG. 6, a method 600 of plasma processing includes astep 601 of providing a substrate including an etchable layer and apatterned mask layer overlying the etchable layer. The patterned masklayer includes a dielectric hard mask, an upper hard mask overlying thedielectric hard mask, and a plurality of openings vertically alignedwith exposed regions of the etchable layer.

The upper hard mask includes a transition metal. In one embodiment, theupper hard mask is a nitride comprising the transition metal. In oneembodiment, the upper hard mask is titanium nitride. In anotherembodiment, the upper hard mask is an oxide comprising the transitionmetal.

The method 600 also includes a step 602 of forming an in-situ protectivelayer over the patterned mask layer and the exposed regions and a step603 of performing a plasma etching step after forming the in-situprotective layer in step 602. Step 603 includes etching the exposedregions of the etchable layer, removing the in-situ protective layer,and retaining the upper hard mask and the dielectric hard mask.

Other steps may also be performed between step 601 and step 602. Forexample, a step of etching the exposed regions of the etchable layerafter providing the substrate and before forming the in-situ protectivelayer may be performed to form initial recesses in the etchable layer.

Example embodiments of the invention are summarized here. Otherembodiments can also be understood from the entirety of thespecification as well as the claims filed herein.

Example 1. A method of plasma etching including: receiving, by a plasmaprocessing apparatus, a substrate into a processing chamber of theplasma processing apparatus, the substrate including an etchable layerand a first mask layer overlying the etchable layer, the first masklayer including a plurality of openings vertically aligned with exposedregions of the etchable layer; forming, in the processing chamber, aprotective layer over the first mask layer and the exposed regions; andetching, in the processing chamber, the protective layer and the exposedregions to remove the protective layer and form recesses in the etchablelayer.

Example 2. The method of example 1, where: the substrate furtherincludes a second mask layer between the first mask layer and theetchable layer, the openings extending through both the first mask layerand the second mask layer; the first mask layer includes a metal, metaloxide, or metal nitride; and the second mask layer includes adielectric.

Example 3. The method of one of examples 1 and 2, where: the recessesinclude a first lateral width and a vertical depth, the first lateralwidth being less than half of the vertical depth; and the first masklayer includes a second lateral width separating adjacent openings ofthe plurality of openings and substantially equal to the first lateralwidth.

Example 4. The method of example 3, where the first lateral width andthe second lateral width are less than 25 nm.

Example 5. The method of one of examples 1 to 4, further including:creating a vacuum in the processing chamber before forming theprotective layer; and where both forming the protective layer andetching the protective layer and the exposed regions are performedwithout breaking the vacuum.

Example 6. The method of one of examples 1 to 5, further including:cyclically performing forming, in the processing chamber an additionalprotective layer over the first mask layer and the recesses in theetchable layer, and etching, in the processing chamber, the additionalprotective layer and the etchable layer in the recesses to remove theadditional protective layer and increase a vertical depth of therecesses.

Example 7. The method of one of examples 1 to 6, further including:etching, in the processing chamber, the exposed regions of the etchablelayer after receiving the substrate and before forming the protectivelayer.

Example 8. The method of one of examples 1 to 7, where: the first masklayer includes a first vertical thickness before forming the protectivelayer; the first mask layer includes a second vertical thickness afteretching the protective layer and the exposed regions; and the secondvertical thickness is greater than 60% of the first vertical thickness.

Example 9. A method of plasma processing including: in-situ during aplasma etch, forming a protective layer over a patterned mask layer andexposed regions of an etchable layer of a substrate, the protectivelayer including a first thickness measured from upper surfaces of thepatterned mask layer and a second thickness measured from exposedsurfaces of the exposed regions, where the first thickness is greaterthan the second thickness; and in-situ during the plasma etch,concurrently removing the protective layer and etching the etchablelayer of the substrate at the exposed regions.

Example 10. The method of example 9, where the first thickness isbetween about 1 nm and about 10 nm.

Example 11. The method of one of examples 9 and 10, further includingcyclically performing the steps of: in-situ during the plasma etch,forming the protective layer; and in-situ during the plasma etch,concurrently removing the protective layer and etching the etchablelayer of the substrate at the exposed regions.

Example 12. The method of one of examples 9 to 11, further including:in-situ during the plasma etch, etching the etchable layer of thesubstrate at the exposed regions before forming the protective layer.

Example 13. The method of one of examples 9 to 12, where forming theprotective layer includes forming the protective layer over a period ofbetween about 10 s and about 60 s.

Example 14. A method of plasma processing including: providing asubstrate including an etchable layer and a patterned mask layeroverlying the etchable layer, the patterned mask layer including adielectric hard mask, an upper hard mask overlying the dielectric hardmask, the upper hard mask including a metal, metal oxide, or a metalnitride, and a plurality of openings vertically aligned with exposedregions of the etchable layer; forming an in-situ protective layer overthe patterned mask layer and the exposed regions; and performing aplasma etching step including etching the exposed regions of theetchable layer, removing the in-situ protective layer, and retaining theupper hard mask and the dielectric hard mask.

Example 15. The method of example 14, where the upper hard mask includesa transition metal.

Example 16. The method of example 14, where the upper hard mask istitanium nitride.

Example 17. The method of example 14, where the upper hard mask is anoxide including a transition metal.

Example 18. The method of one of examples 14 to 17, further including:etching the exposed regions of the etchable layer after providing thesubstrate and before forming the in-situ protective layer.

Example 19. The method of one of examples 14 to 18, where: the upperhard mask includes a first vertical thickness before forming the in-situprotective layer; the upper hard mask includes a second verticalthickness after performing the plasma etching step; and the secondvertical thickness is greater than 60% of the first vertical thickness.

Example 20. The method of one of examples 14 to 19, where forming thein-situ protective layer includes forming the in-situ protective layerover a period of between about 10 s and about 60 s.

While this invention has been described with reference to illustrativeembodiments, this description is not intended to be construed in alimiting sense. Various modifications and combinations of theillustrative embodiments, as well as other embodiments of the invention,will be apparent to persons skilled in the art upon reference to thedescription. It is therefore intended that the appended claims encompassany such modifications or embodiments.

1. A method of plasma etching comprising: receiving, by a plasmaprocessing apparatus, a substrate into a processing chamber of theplasma processing apparatus, the substrate comprising an etchable layerwhich is a target layer to be etched and a first mask layer overlyingthe etchable layer, the first mask layer comprising a plurality ofopenings vertically aligned with exposed regions of the etchable layer;forming, in the processing chamber, a protective layer over the firstmask layer and the exposed regions, wherein the protection layerprotects the first mask layer; and etching, in the processing chamber,the protective layer and the exposed regions to remove the protectivelayer and form recesses or deepen recesses in the etchable layer;wherein the etching includes a concurrent etching step during which theprotective layer is removed and the etchable layer is concurrentlyetched, and wherein at a start of said concurrent etching step theprotective layer is present on a top of the first mask layer and aftersaid concurrent etching step the top of the first mask layer is exposed.2. The method of claim 1, wherein: the substrate further comprises asecond mask layer between the first mask layer and the etchable layer,the openings extending through both the first mask layer and the secondmask layer; the first mask layer comprises a metal, metal oxide, ormetal nitride; and the second mask layer comprises a dielectric.
 3. Themethod of claim 1, wherein: the recesses comprise a first lateral widthand a vertical depth, the first lateral width being less than half ofthe vertical depth; and the first mask layer comprises a second lateralwidth separating adjacent openings of the plurality of openings andsubstantially equal to the first lateral width.
 4. The method of claim3, wherein the first lateral width and the second lateral width are lessthan 25 nm.
 5. The method of claim 1, further comprising: creating avacuum in the processing chamber before forming the protective layer;and wherein both forming the protective layer and etching the protectivelayer and the exposed regions are performed without breaking the vacuum.6. The method of claim 1, further comprising: cyclically performingforming, in the processing chamber an additional protective layer overthe first mask layer and the recesses in the etchable layer, andetching, in the processing chamber, the additional protective layer andthe etchable layer in the recesses to remove the additional protectivelayer and increase a vertical depth of the recesses.
 7. The method ofclaim 1, further comprising: etching, in the processing chamber, theexposed regions of the etchable layer after receiving the substrate andbefore forming the protective layer.
 8. The method of claim 1, wherein:the first mask layer comprises a first vertical thickness before formingthe protective layer; the first mask layer comprises a second verticalthickness after the concurrent etching step, wherein the second verticalthickness is less than the first vertical thickness; and the secondvertical thickness is greater than 60% of the first vertical thickness.9. A method of plasma processing comprising: in-situ forming aprotective layer over a patterned mask layer and exposed regions of anetchable layer of a substrate such that the protective layer protectsthe patterned mask layer, and wherein the etchable layer is a targetlayer to be etched, the protective layer comprising a first thicknessmeasured from upper surfaces of the patterned mask layer and a secondthickness measured from exposed surfaces of the exposed regions, whereinthe first thickness is greater than the second thickness, and whereinthe first thickness is between about 1 nm and about 10 nm; and in-situperforming a concurrent plasma etch of concurrently removing theprotective layer and etching the etchable layer of the substrate at theexposed regions.
 10. (canceled)
 11. The method of claim 9, furthercomprising cyclically performing the steps of: in-situ forming theprotective layer; and in-situ performing the concurrent plasma etch,concurrently removing the protective layer and etching the etchablelayer of the substrate at the exposed regions.
 12. The method of claim9, further comprising: in-situ, etching the etchable layer of thesubstrate at the exposed regions before forming the protective layer.13. The method of claim 9, wherein forming the protective layercomprises forming the protective layer over a period of between about 10s and about 60 s.
 14. A method of plasma processing comprising:providing a substrate comprising an etchable layer which is a targetlayer to be etched and a patterned mask layer overlying the etchablelayer, the patterned mask layer comprising a dielectric hard mask, anupper hard mask overlying the dielectric hard mask, the upper hard maskcomprising a metal, metal oxide, or a metal nitride, and a plurality ofopenings vertically aligned with exposed regions of the etchable layer;forming an in-situ protective layer over the patterned mask layer andthe exposed regions such that the in-situ protective layer protects thepatterned mask layer; and performing a plasma etching step, wherein theplasma etching step is a concurrent plasma etch step during which: (i)the in-situ protective layer is removed, (ii) the etchable layer isetched, and (iii) a portion of the upper hard mask is removed with atleast 50% of a vertical thickness of the upper hard mask remaining afterthe concurrent plasma etch step compared to prior to the concurrentplasma etch step.
 15. The method of claim 14, wherein the upper hardmask comprises a transition metal.
 16. The method of claim 14, whereinthe upper hard mask is titanium nitride.
 17. The method of claim 14,wherein the upper hard mask is an oxide comprising a transition metal.18. The method of claim 14, further comprising: etching the exposedregions of the etchable layer after providing the substrate and beforeforming the in-situ protective layer.
 19. The method of claim 14,wherein: the upper hard mask comprises a first vertical thickness beforeforming the in-situ protective layer; the upper hard mask comprises asecond vertical thickness after performing the plasma etching step; andthe second vertical thickness is greater than 60% of the first verticalthickness.
 20. The method of claim 14, wherein forming the in-situprotective layer comprises forming the in-situ protective layer over aperiod of between about 10 s and about 60 s.
 21. The method of claim 2,wherein: the first mask layer comprises a transition metal; theprotective layer comprises at least one of silicon oxide, siliconnitride, an organic polymer or a fluorocarbon polymer; at a start ofsaid concurrent etching step the protective layer is present on a top ofthe first mask layer with a thickness of between about 1 nm and about 10nm, and the protective layer is present on a top of the exposed surfaceswith a thickness of the less than the thickness on top of the first masklayer; and wherein during said concurrent etching step a portion of thefirst mask layer is a removed and a vertical thickness of the first masklayer is 50% or larger upon completion of the concurrent etching stepcompared to the vertical thickness prior to the concurrent etching step.22. The method of claim 9, wherein during the concurrent plasma etch aportion of the patterned mask layer is removed and the patterned masklayer has a vertical thickness 50% or more after the concurrent plasmaetch compared to prior to the concurrent plasma etch.
 23. The method ofclaim 14, wherein at a start of said concurrrent plasma etch, thein-situ protective layer is present on top of the upper hard mask and ontop of the exposed regions of the etchable layer with a thickness of thein-situ protective layer larger on top of the upper hard mask than ontop of the exposed regions of the etchable layer.
 24. The method ofclaim 23, wherein the upper hard mask includes a transition metal,wherein at the start of said concurrent plasma etch the thickness of thein-situ protective layer has a thickness on top of the upper hard maskwhich is between about 1 nm and about 10 nm.